The present invention relates to a method of controlling supercharging pressure in internal combustion engines, and more particularly to a method of properly controlling supercharging pressure in a transitional state.
Conventionally, a method of controlling supercharging pressure for internal combustion engines installed on automotive vehicles has been proposed by the assignee of the present application, e.g. in Japanese Provisional Patent Publication (Kokai) No. 63129126 in which supercharging pressure is controlled in open loop control mode when supercharging pressure is in a transitional state in which supercharging pressure is drastically increased, and controlled in feedback control mode when supercharging pressure is in a steady state in which the supercharging pressure is not drastically changed though it is somewhat changed, whereby smooth supercharging pressure control is carried out while preventing hunting of supercharging pressure due to time lag in the responsiveness of the control system.
Further, another method of controlling supercharging pressure has been proposed by the assignee of the present application, e.g. in Japanese Provisional Patent Publication (Kokai) No. 63-129127 in which the control amount of supercharging pressure in the open loop control mode is set in accordance with a learned correction value calculated during the feedback control mode for the purpose of compensating for deviation in the supercharging pressure control due to variation in performance between control system lots manufactured by mass-production or aging of the control system. Particularly, according to this proposed method, in view of great influence of the intake air temperature on supercharging pressure, the learned correction value is separately calculated for each of regions divided in accordance with the intake air temperature.
However, the above-described control methods have the following disadvantages in properly controlling the supercharging pressure in the transitional state.
Specifically, in the feedback control region in which the learned correction value is calculated, the supercharging pressure is in a steady state. However, when the supercharging pressure in the steady state, even if the engine is in the same operating region which is determined by the intake air temperature, the supercharging pressure is not constant. For example, if the desired value of the supercharging pressure as the target value of the feedback control is set to a value different from a normal value, the actual supercharging pressure is changed as the desired value of the supercharging pressure is set to different values. However, in the above-described conventional control methods, if the supercharging pressure is in the steady state, the learned correction value is always calculated in each operating region of the engine determined by the intake air temperature, irrespective of whether the supercharging pressure is changed as described above. As a result, the learned correction value calculated in such changed state of the supercharging pressure shows different values in the same operating region of the engine. Since in the open loop control the control amount of the supercharging pressure is set in accordance with the learned correction value thus calculated, there will be a deviation of the supercharging pressure from the proper desired value, and hence it is impossible to properly carry out control of the supercharging pressure.